In those industries, it is common to use materials resulting from products of natural or synthetic origin which are of polymeric or monomeric structure and which comprise at least two carboxylic functional groups. All or part of these functional groups can exist in either the “free acid” (COOH) form or other forms, in particular in the form of associated salts, such as alkali metal or alkaline earth metal salts. These materials, which can be described as “polycarboxylates”, can be used in particular as chelating or sequestering agents for metals, detergency builders or cobuilders, or agents which delay the setting of hydraulic binders but also as stabilizing, structuring, dispersing, disintegrating or stripping agents for compositions of any nature and destination.
They can consist of natural products derivatives, such as poly- and monosaccharides, in particular of starch derivatives or of starch-hydrolyzed products.
They can be, inter alia:                carboxyalkylated derivatives of starch hydrolysates,        glucuronyl-arabinarates or glucuronyl-glucarates, obtained from starch hydrolysates,        glucuronyl-glucaric acid, glucaric acid or mannaric acid, obtained respectively from maltitol, sorbitol or mannitol,the preparation and the uses of such polycarboxylates resulting from natural products being disclosed in particular in patents WO 95/02614, EP 780 399 and EP 798 310 on behalf of the Applicant Company and, for example, in patent EP 656 051.        
Other monomeric or polymeric polycarboxylates result from products of synthetic or natural origin that are of non-saccharide nature, such as, for example:                dicarboxylic acids, such as tartaric acid, succinic acid or glutaric acid,        tricarboxylic acids, such as citric acid or nitrilotriacetic acid (“NTA”),        tetracarboxylic acids, such as ethylenediamine-tetraacetic acid (“EDTA”),        (co) polymers of ethylenic carboxylic acids, such as, for example, polyacrylates,the uses of such polycarboxylates resulting from products of non-saccharide nature being, inter alia, disclosed in patents FR 2 657 601, FR 2 735 788, WO 91/00901, EP 565 266, EP 605 318, EP 650 941 or EP 972 825.        
In view of the current restrictions for the protection of the human life and the environment, it is advisable to have available polycarboxylates resulting from renewable products of natural origin.
For approximately a decade, numerous studies have focused on several polycarboxylates such as glucaric acid and its salts.
The abovementioned patent EP 656 051 discloses the preparation of phosphate-free detergents based on zeolites and/or on lamellar silicates comprising, as complexing agents, polyhydroxydicarboxylic acids or polyhydroxydicarboxylic acid salts comprising from 4 to 6 carbon atoms and at least 2 hydroxyl groups per molecule, such as, in particular, sodium glucarate and sodium galactarate.
The abovementioned patent EP 798 310, published on behalf of the Applicant Company, discloses, in its Example 1, the preparation of a composition comprising 33% of glucaric acid in the form of its sodium salt and 67% of sodium chloride, with the absence of products from the overoxidation of glucaric acid. This composition, which has high content of NaCl, is obtained by oxidation of sorbitol by sodium hypochlorite (NaOCl or “bleach”) in the presence of a catalyst composed of a binary or tertiary alkyl nitroxy, such as 2,2,6,6-tetramethylpiperidinyloxy or “TEMPO”.
More recently, other studies have been described in the paper by J. F. Thaburet et al. entitled “TEMPO-mediated oxidation of maltodextrins and D-glucose: effect of pH on the selectivity and sequestering ability of the resulting polycarboxylates”, Carbohydrate Research, 330 (2001), pp. 21-29.
These studies have shown that the oxidation of glucose or sorbitol in the presence of TEMPO and NaOCl was particularly difficult to control. Nevertheless it was possible to obtain a good yield (90%) of glucaric acid under very specific conditions (including a pH of 11.7 and the necessary presence of sodium bromide NaBr).
Furthermore, this document shows that, depending on the number of equivalents of NaOCl employed, the glucaric acid synthesis results in the preferential coproduction:                either of gluconic acid, i.e. of the monocarboxylic acid corresponding to glucaric acid,        or of other dicarboxylic acids but which are small, namely tartaric acid and oxalic acid.        
The authors believe that the coproduction of these last two acids is due to the oxidative decomposition of the monosaccharide (glucose, sorbitol) at two breakdown on the molecule, namely a) between the C-4 and C-5 carbon atoms and b) between the C-2 and C-3 carbon atoms.
More recently still, other pathways for the decomposition of glucaric acid have been suggested, as an attempt to explain the coproduction of meso-tartaric acid or of D-tartaric acid during the oxidation of glucose to glucaric acid in the presence of NaOCl, NaBr and TEMPO.
These decomposition pathways, hypothetical or otherwise, are described in the very recent paper by M. Ibert et al. entitled “Determination of the side-products formed during the nitroxide-mediated bleach oxidation of glucose to glucaric acid”, Carbohydrate Research, 337 (2002), pp. 1059-1063.
In any case, in view of the above there is a number of drawbacks in the preparation of dicarboxylic acid, such as glucaric acid, from a monosaccharide, such as glucose, which may be optionally hydrogenated (sorbitol), and in particular:                the use of sodium hypochlorite, which is not desirable because of the current restrictions for the protection of human life and the environment,        the possible use of NaBr, that is not desirable given its capacity to generate halogenated entities,        the need to closely monitor and control the reaction parameters, such as the pH and the concentration of NaOCl, in order to obtain a minimum or acceptable yield of desired product,        the significant and undesired coproduction either of not profitable materials (NaCl) or monocarboxylic materials (gluconic acid and its salts) or dicarboxylic materials (oxalic and tartaric acids and their salts). These materials have a (very) greatly reduced molecular weight due to decomposition. They also have few (tartaric acid) or no (oxalic acid) OH groups. The presence of these materials reduces the properties, in particular the chelating or sequestering properties, of the glucaric acid composition.        
In addition to these problems regarding the generation of decomposition products, the oxidation of mono-saccharides with TEMPO and sodium hypochlorite does not make it possible to obtain materials having three carboxylic functional groups, as is the case, with polycarboxylates commonly used in industry, such as citric acid and citrates.